Antireflective coatings may be useful for photovoltaic devices and other applications in which reflection of electromagnetic radiation is preferably avoided. Titania-based coatings may be used, although they occasionally may suffer from possible disadvantages, such as instability of coating solutions or sols.
Conventional wet chemical methods to produce titania coatings may use sol-gel processes involving hydrolysis and/or condensation reactions of titanium alkoxides. Titania coatings that are formed from these sols are generally fired at elevated temperatures to convert the precursor compounds into titanium dioxide coatings. In many instances, titania sols are aged for several hours after they are prepared in order to ensure thorough hydrolysis of precursor alkoxides.
The stability of titania sols may be affected by several factors, including pH, water content, concentration of solids, etc. Chelating ligands, such as 2,4-pentanedione may be added to titania sols so as to prolong their shelf life.
Producing stable sols in volumes required for mass production may be challenging. While the shelf life of titania sols may be influenced by storage and transportation conditions, the useful pot life during processing may be affected by the loss of volatiles, exposure to humidity (e.g., ambient humidity), etc. During thermal processing of coatings, heating profiles of gradual temperature ramp rates may be employed to promote condensation and cross-linking reactions. Coatings may be fired at high temperatures to burn off organic content and form titanium dioxide coatings.
Thus, there may be a need for a method to produce stable titania precursor formulations, which may remain largely unaffected by variations in temperature and humidity during storage, transportation, and processing. There may also be a need for a method by which titania coatings could be formed without the need for initial thermal processing prior to high temperature densification. There may also be a need for a method by which titania precursor coatings may be stored and fired on demand to produce titania coatings.
Hydrophilic coatings (e.g., coatings with a low contact angle) may be useful for self-cleaning surfaces as well as in anti-fog and/or anti-mist applications. Antireflective coatings may be useful for photovoltaic devices and other applications in which reflection of electromagnetic radiation is preferably avoided.
Photovoltaic devices such as solar cells (and modules therefor) are known in the art. Glass is an integral part of most common commercial photovoltaic modules, including both crystalline and thin film types. A solar cell/module may include, for example, a photoelectric transfer film made up of one or more layers located between a pair of substrates. One or more of the substrates may be of glass, and the photoelectric transfer film (typically semiconductor) is for converting solar energy to electricity. Example solar cells are disclosed in U.S. Pat. Nos. 4,510,344, 4,806,436, 6,506,622, 5,977,477, and JP 07-122764, the disclosures of which are hereby incorporated herein by reference.
For photovoltaic (PV) applications—that is, in applications involving photovoltaic modules—the reflection of glass is preferably minimized. It is clear the power output of the module is dependant upon the amount of light (e.g., the number of photons) within the solar spectrum that passes through the glass and reaches the PV semiconductor. Therefore, numerous attempts have been made to try to boost overall solar transmission through glass used in PV-modules.
One attempt relates to the use of iron-free or “clear” glass, which may increase the amount of solar light transmission when compared to regular float glass, through absorption minimization. Solar transmission may be further increased by the use of an antireflective (AR) coating on the first surface of the glass. Porous silica has been used as an AR coating on a glass substrate. But AR coatings derived from porous silica may be difficult to keep clean due to the possible a presence of a large amount of pores in structure.
Therefore, there may be a need to include a antireflective coating. Such a coating may be highly durable and/or self cleaning and/or hydrophilic and may be used as a PV superstrate.
In an example embodiment of this invention, there is provided a method of making a coated article including a coating. The method may comprise mixing a photomonomer comprising at least one radiation curable monomer capable of polymerization through exposure to ultraviolet radiation or electron beams with a titanium alkoxide to form a mixture; and applying the mixture directly or indirectly on a substrate and curing the mixture through exposure to ultraviolet radiation or electron beams after its application so as to form a titanium dioxide layer on the substrate.
In an example embodiment of this invention, there is a coated article comprising a substrate and a titanium dioxide coating, wherein the titanium dioxide coating comprises a layer comprising a polymerized photomonomer and titanium dioxide.
In an example embodiment of this invention, there is provided a method of making a photovoltaic device including a titania-based coating. The method may comprise: mixing a photomonomer comprising at least one radiation curable monomer capable of polymerization through exposure to ultraviolet radiation or electron beams with a titanium alkoxide to form a mixture; applying the mixture directly or indirectly on a glass substrate; curing the mixture through exposure to ultraviolet radiation or electron beams after its application; firing the coating layer in an oven at a temperature of from about 550 to 700° C. for a duration of from about 1 to 10 minutes; and using the glass substrate with the coating layer thereon as a front glass substrate of the photovoltaic device so that the titania-based coating is provided on a light incident side of the glass substrate.
In an example embodiment of this invention, there is provided a method of making a photovoltaic device comprising: a photovoltaic film, and at least a glass substrate on a light incident side of the photovoltaic film; an antireflection coating provided on the glass substrate; wherein the antireflection coating comprises at least a layer produced using a method comprising the steps of: mixing a photomonomer comprising at least one radiation curable monomer capable of polymerization through exposure to ultraviolet radiation or electron beams with a titanium alkoxide to form a mixture; applying the mixture directly or indirectly on a glass substrate; curing the mixture through exposure to ultraviolet radiation or electron beams after its application; and firing the coating layer in an oven at a temperature of from about 550 to 700° C. for a duration of from about 1 to 10 minutes.
In an example embodiment of this invention, there is provided a method of making a coated article comprising: a glass substrate; a photocatalytic and hydrophilic coating provided on the glass substrate; wherein the photocatalytic and hydrophilic coating comprises at least a layer produced using a method comprising the steps of: mixing a photomonomer comprising at least one radiation curable monomer capable of polymerization through exposure to ultraviolet radiation or electron beams with a titanium alkoxide to form a mixture; applying the mixture directly or indirectly on a glass substrate; curing the mixture through exposure to ultraviolet radiation or electron beams after its application; and firing the coating layer in an oven at a temperature of from about 550 to 700° C. for a duration of from about 1 to 10 minutes.